I'm pretty sure it should just be /user/ to bring you to a login page.

I'm not sure why that is coming up broken on different pages. That's a separate problem. That page won't come up at all for this particular issue once the link is fixed from /user/... to /forum/... for viewing the member profiles.

Where are you getting a link to the /forum/ instead of /user/? When I clicked on your linked username, it went (correctly) to /user/

I got to the error by clicking Kisshu's picture in the Jdrama group, THEN clicking on the "forum user profile" link at the bottom of her user profile.

http://www.thejapanesepage.com/user/6156 (when you click her picture) goes to the correct user profile for drupal, but then the forum user profile link at the bottom of that page, which should take you to the forum user profile, is a broken mix of both links (as described ad nauseum up above).